Speed sensor and method of attaching the same

ABSTRACT

A speed sensor (B, C) produces a signal that reflects the angular velocity of a shaft ( 4 ) which rotates in a case ( 2 ) having a mounting surface ( 10 ), beyond which the shaft projects to provide a target ( 6 ), and threaded holes ( 12 ) which open out of the mounting surface. The speed sensor includes a housing ( 20 ) and a sensing element ( 22 ) which is embedded in the housing. The housing, which is formed from a deformable material, has slots ( 44, 60 ) which align with the threaded holes in the case, and receive screws ( 24, 66 ) which thread into the holes to secure the speed sensor to the case. The speed sensor is positioned such that the proper air gap exists between its sensing element and the target. The screws, which extend through the slots, produce indentations ( 56, 74 ) in the deformable material of the housing, and these indentations receive the screws, so that the position of the sensor is fixed. Thus, the sensor, if removed, may be reinstalled in the same location.

CROSS REFERENCE TO RELATED APPLICATIONS

This application derives priority from United States provisionalapplication Ser. No. 60/396,587, filed 17 Jul. 2002, for the inventionof Wayne V. Denny, Kevin Rehfus and Richard Smith entitled “Means forAttaching a Sensor”.

TECHNICAL FIELD

This invention relates in general to speed sensors for monitoring theangular velocities of rotating devices, and more particularly to a speedsensor, which, once installed, may be reinstalled in the same location,and to a process for installing a speed sensor.

BACKGROUND ART

A variety of sensors exist for monitoring the angular velocities ofrotating shafts—sensors which are connected to control systems that inone way or another control the operation of such shafts or other machineelements. The typical sensor mounts on a stationary component of amachine opposite a shaft which rotates in that component. The shaftcarries a target along its periphery, and the target has the capacity toproduce a pulsating signal in the sensor, which signal is monitored bythe control system. The target may take the form of alternating ridgesand valleys on a gear or spline, or may take the form of a keyway oreven pins. It may also assume a magnetic form, consisting of magneticpoles. Sensors assume two basic forms—passive and active. A passivesensor does not require any power from the control system to operate it.But it does require a very small and accurate air gap, and it will notregister credible speeds at low angular velocities. A variablereluctance sensor represents one type of passive sensor. An activesensor requires power from the control system and will operateeffectively with larger air gaps and at lower speeds. Active sensors arebetter suited for traction control systems and in assemblies where theair gap is difficult to accurately control. Moreover, some activesensors can sense direction. A Hall-effect sensor represents one type ofactive sensor.

For a sensor to operate effectively, the air gap between it and thetarget that it monitors must fall within prescribed tolerances. Thisrequires a good measure of precision during the manufacture of thesensor and the component on which it is installed, or during theinstallation of the sensor, or both. These exacting demands must also bemet during subsequent maintenance procedures which require removal ofthe sensor and reinstallation. In one type of sensor mounting a hardstop on the sensor seats against a surface on the stationary machinecomponent, thus controlling an air gap with a good measure of precision.The sensor may be removed and reinstalled without too much concern aboutaltering the air gap. However, the sensor and the seat against which itshard stop bears must be manufactured with considerable precision. When asensor is mounted on a surface that lies perpendicular to or at asubstantial angle to the axis of the shaft, no hard stop or seat existsto fix the position of the sensor, while the original installation ofsuch a sensor may be easy, without a hard stop, the reinstallation ofthe sensor after a maintenance procedure requires exacting efforts.

SUMMARY OF THE INVENTION

The present invention resides in a speed sensor which is attached to amounting surface with at least one screw that extends through a slot inthe sensor. The screw creates an indentation along the slot, and theindentation serves to locate the sensor in the same position when thesensor is removed and later reinstalled. The invention also resides inthe process for installing the sensor, using the screw to create anindentation in the sensor.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a machine provided with a speed sensorconstructed and installed in accordance with the present invention;

FIG. 2 is a front elevational view of the sensor;

FIG. 3 is a side elevational view of the sensor;

FIG. 4 is a front end elevational view of the sensor;

FIG. 5 is a rear elevational view of the sensor;

FIG. 6 is a fragmentary sectional view of the sensor taken along line6-6 of FIG. 2;

FIG. 7 is an exploded perspective view of the machine and sensor showingthe sensor upon being prepared for reinstallation with the indentationsin the rims surrounding its slots serving to locate the sensor in theproper position;

FIG. 8 is a fragmentary plan view showing the indentation along one ofthe slots and the position assumed by the screw in those indentations;

FIG. 9 is a plan view of a modified speed sensor embodying the presentinvention;

FIG. 10 is a fragmentary sectional view taken along line 10-10 of FIG.9;

FIG. 11 is a perspective view showing the modified sensor installed in amachine; and

FIG. 12 is a plan view of the modified sensor showing the indentationsformed by the screws which mount it.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the drawings, a machine A (FIG. 1) includes astationary housing or case 2 in which a shaft 4 rotates about an axis X.The shaft 4 carries a target 6 which rotates with it, and the rotationof the target 6—and likewise the shaft 4—is monitored by a speed sensorB which is attached to the case 2. The sensor B, in response to therotation of the target 6, produces a pulsating signal, which reflectsthe angular velocity of the shaft 4. Indeed, the sensor B may beconnected to a control system which controls the speed at which theshaft 4 rotates or the function of some other machine element.

Briefly, the case 2 is preferably a metal casting which is machinedalong appropriate surfaces. One of those surfaces is a mounting surface10 beyond which the shaft 4 projects. The surface 10 lies perpendicularto the axis X of the shaft 4, or at least at a steep angle with respectto the axis X. The case 2 contains at least two threaded holes 12 (FIG.7) which open out of the surface 10, yet lie parallel to the axis X. Thetarget 6 encircles the shaft 4 adjacent to where the shaft 4 emergesfrom the surface 10 of the case 2. The target 6 possesses a successionof ribs or teeth 14 which are arranged in a pattern around the axisX—most often at equal circumferential intervals—and as such areseparated by axially directed grooves 16. The outermost surfaces of theribs or teeth 14 describe a circle—or, more accurately, acylinder—having its center at the axis X.

The sensor B includes (FIG. 2) a housing 20, which is preferably moldedfrom a polymer, and a sensing element 22 which is embedded in thehousing 20, preferably with the housing 20 over-molded around thesensing element 22. The sensor B is secured to the case 2 with machinescrews 24 (FIGS. 1 & 7) having shanks 26 which thread into the holes 12.The screws 24 at the ends of their shanks 26 have heads 28 provided withcircular peripheries, and those heads 28 bear firmly against the housing20 of the sensor B to hold the sensor B in place.

The housing 20 has (FIGS. 2-5) a raised central portion 30 and twoflanges 32 which project laterally from the central portion 30. Acrossthe central portion 30 and the two flanges 32 extends a planar back face34 which bears against the mounting surface 10 of the case 2. Thecentral portion 30 has an end face 36 which is presented toward axis Xand the target 6. The central portion 30 also contains a cylindricalbore 38 which opens out of the end face 36. Indeed, the bore 38 extendsout into a sacrificial layer or rim 40 which projects beyond the endface 36.

Each flange 32 possesses (FIGS. 2-5) a front face 42 which lies parallelto the back face 34. Moreover, each contains a slot 44 that extendscompletely through it from its front face 42 to its back face 36, withthe major axis of the slot 44 being parallel to the axis of the bore 38.The two slots 44 are wide enough to loosely receive the threaded shanks26 of the machine screws 24, but not the heads 28 of the screws 24, andare spaced apart a distance corresponding to the spacing between thethreaded holes 12 in the case 2. Each slot 44 is surrounded by a rim 46which projects away from the front face 42 of its flange 32 (FIG. 6),yet is formed integral with the flange 32. The inside face of the rim 46for each flange 32 lies flush with the surface of its slot 44.Typically, the thickness of each rim 46 should be between 0.038 and0.042 in. and its height should likewise be between 0.038 and 0.042 in.

The rims 46 at least should be formed from a deformable material whichcan be permanently crushed to create an indentation that corresponds insize to the implement used to crush it. Certain polymers are suitablefor this deformable material, among which are PVC, acetal, nylon andPCS. Some metals of a ductile character will also suffice. Thedeformable material enables the rims46 to serve as crush pads. As apractical matter, the entire housing 20 is formed as an integral unitfrom the deformable material.

The sensing element 22 is embedded within central portion 30 of thehousing 20 (FIGS. 2 & 4) and for the most part is generally cylindrical.It aligns with the cylindrical bore 38 that opens out of the end face 36and has a sensing face 50 which is exposed through the bore 38. Indeed,the sensing face 50 lies a prescribed distance from the end of thesacrificial rim 40 on the housing 20, and that distance corresponds tothe air gap at which the sensing element 22 will operate mosteffectively. The sensing element 22 also includes a cable 52 whichemerges from the central portion 30 of the housing 20 and delivers thesignal produced by the sensing element 22 to a control system.

The sensing element 32 may assume any of several common designs. It maybe passive or active, whatever best suits the conditions under which itis to operate and the speed of the target 6. Those that operate on theHall-effect principle are particularly suited for the sensing element32, although variable reluctance and magneto resistive sensors will alsosuffice as will others.

To install the senor B on the case 2 of the machine A, the slots 44 inthe flanges 32 of the sensor B are aligned with the threaded holes 12 inthe case 2, with the back face 34 of the sensor housing 20 presentedtoward the planar mounting surface 10 on the case 2 and the sacrificialrim 40 that is around the bore 38 presented toward the target 6.

Thereupon, the shanks 26 of the machine screws 24 are inserted throughthe slots 44 in the flanges 32 of the sensor B and engaged with thethreads of the threaded holes 12. The screws 24 are turned down untilthe undersides of their heads 28 bear lightly against the rims 46 thatsurround the slots 44. This brings the back face 34 of the sensorhousing 20 lightly against the mounting surface 10 on the case 2. Theclamping force produced by the screws 24 at this juncture is perhapslarge enough to prevent the sensor B for changing position under its wonweight, but is not great enough to prevent a light manually exertedforce from displacing the sensor B, nor is it great enough to deform therims 46 that surround the slots 44. Next the sensor B is manuallyadjusted to bring the sacrificial rim 40 on its housing 20 against thetarget 6—specifically, against the teeth 14 that form the target 6. Thisestablishes the correct air gap between the sensing face 50 of thesensing element 22 and the circle described by the teeth 14 of thetarget 6. With the sensor B so positioned, the machine screws 24 aretightened. As the screws 24 are turned downwardly, their heads 26 sinkinto and crush or otherwise permanently deform the rims 46 that surroundthe slots 44, but only where the undersides of the heads 26 contact therims 46. Elsewhere, the rims 46 remain intact and in their originalconfigurations. In other words, the heads 26 of the screws 24 createpermanent indentations 56 (FIGS. 7 & 8) in the rims 46 that surround theslots 44. The force exerted by the screws 24 on the housing 20 of thesensor B forces the back face 34 of the housing 20 firmly against themounting surface 10 on the case 2, and the friction between the face 34and surface 20 alone is enough to hold the sensor B in place on the case2. But the location of the sensor B is further secured by virtue of theheads 26 of the screws 24 being snugly received in the indentations 56formed in the rims 46 that surround the slots 44 (FIG. 8).

When the shaft 4 begins to rotate, the teeth 14 of the target 14 mayabrade the sacrificial rim 40 at the end face 36 of the sensor housing20, but only a minute quantity of the material from which the housing 20is formed wears away. The air gap between the sensing face 50 of thesensor element 22 and the circle described by the teeth 14 of the target6 remains unchanged and at the dimension best suited for operation ofthe sensor B.

As the teeth M on the rotating target 6 pass by the sensing face 50 ofthe sensing element 22, they disturb a magnetic field created by thesensing element 32, and the sensing element 22 detects thesedisturbances, producing a pulsating electrical signal that reflects theangular velocity of the target 6 and the shaft 4 which carries thetarget 6. Depending on its type, the sensor 22 may also register thedirection of rotation.

Should it become necessary to remove the sensor B to perform maintenanceon it or other components of the machine A, the screws 24 which hold thesensor B in place are simply backed off and removed from their holes 12in the case 2. This frees the sensor B from the case 2. Once themaintenance is complete, the sensor B is again placed against the case 2and the screws 24 are inserted in the holes 12 in the housing 20.Instead of realigning and repositioning the sensor B with respect to thetarget 6, the sensor B is simply maneuvered until the indentations 56 inthe rims 46 surrounding its slots 44 lie beneath the heads 28 of thescrews 24 (FIG. 7). Thereupon, the screws 24 are turned down. Theirheads 28 enter the indentations 56 in the rims 46 and position thesensor B in essentially the same location that it had before, so the airgap remains functionally unchanged. This holds true irrespective ofwhether the sensor B was installed initially with the use of thesacrificial rim 40.

A modified sensor C (FIGS. 9-12) likewise has a housing 20 provided witha central portion 30 and flanges 32 projecting from the central portion30 and, in addition, likewise has a sensing element 22 embedded withinthe central portion 30 of the housing 20. The flanges 32 contain slots60 provided with side walls 62. The slots 60 are similar to the slots 32for the sensor B in the sense that the spacing between them equals thespacing between the threaded holes 12 in the case 2, but they differ inthat their side walls 62 taper downwardly toward the back face 34 (FIG.10), so that the slots 60 are narrower at the back face 34 than at thefront faces 42 of the flanges 32. Indeed, at the back face 34 the slots44 are narrower than the diameter of the threaded holes 12.

The sensor C is secured to the case 2 with machine screws 66 which maydiffer from their counterparts for the sensor B. To be sure, each screw66 has a threaded shank 68 and a head 70 at one end of the shank 68. Inaddition, each screw 66 has a cylindrical pilot 72 extended from theother end of its shank 68. The head 70 is too large to pass through theslot 60 or even enter the slot 60. However, the pilot 72 is small enoughto pass into and through the slot 60 and is also small enough to enterthe threaded hole 12, but only with a slight clearance. The threadedshank 68, while being sized and otherwise configured to engage thethreads of the threaded holes 12, is small enough to enter the slot 60at the front face 42 of the flange 32 in which the slot 60 is located,but is too large to pass completely through the slot 60, this being byreason of the taper of the walls 62 for the slot 60. The housing 20 forthe sensor C, at least along the side walls 62 of its slots 60, isformed from a deformable material—one which can be easily broken away orotherwise displaced to create an indentation that corresponds to theimplement used to effect the deformation.

To install the sensor C on the case 2, the sensor housing 20 is placedagainst the mounting surface 10 on the case 2 with the slots 60 in itsflanges 32 aligned with the threaded holes 12 in the case (FIG. 11).Then the screws 66 are inserted into the slots 60 with their pilots 72leading and aligned with the threaded holes 12. The pilots 72 enter theholes 12, thus allowing the threaded shanks 68 to advance into the slots60 until they are restrained by the tapered side walls 62. Thereupon,the sensor C is manipulated manually until it assumes the properposition—one in which the correct air gap exists between the sensingface 5 of the sensing element 32 and the teeth 14 on the target 6—andthe sacrificial rim 40 may be used to this end. Once the sensor Cassumes the correct position, the screws 66 are forced inwardly into thethreaded holes 12. The threaded shanks 68 break through the side walls62 of the slots 60, creating indentations 74 (FIG. 12) that receive thethreaded shanks 72. This allows the thread shanks 72 to pass completelythrough the slots 60 to the holes 12, whereupon when turned, they engagethe threads of the holes 12. The screws 66 are rotated until their heads70 seat firmly against the front faces 42 of the flanges 32.

The indentations 74 serve to locate the sensor C in precisely the sameposition on the case 2 if the sensor C needs to be removed.

The housings 20 of the sensors B and C may be constructed with singleslot 44 or 60 and secured with a single screw 24 or 60, in which event apin or surface may be used to prevent the sensor B or C from rotatingabout a single screw 24 or 66. On the other hand, two screws 24 or 66may be located in a single slot 44 or 60. The target, which the sensorsB or C, monitor may have magnetic poles instead of teeth 14. Also, thetarget 6, which the sensor B monitors, need not be on a shaft 4 thatemerges from the surface 10 of the case 2, but may be on a rotatingdevice that revolves adjacent to or near the surface 10.

1. In combination with a mounting surface out of which a threaded holeopens and with a target which rotates in front of the surface about anaxis that is oriented at a steep angle with respect to the surface, andwith a screw having a threaded shank that threads into the hole and ahead at the end of the shank; a sensor for monitoring the rotation ofthe target; said sensor comprising: a housing located along the mountingsurface and having a slot that is aligned with the threaded hole, thehousing along the slot being formed from a deformable material andcontaining a permanent indentation that receives a portion of the screw,the indentation having been formed by the screw itself and being of aconfiguration that prevents displacement of the slot along the screwwhen the portion of the screw is in the indentation; and a sensingelement located in the housing and being capable, in response torotation of the target, of producing a signal that reflects the angularvelocity of the target; whereby the sensor, should it be removed fromthe mounting surface by withdrawing the screw from the threaded hole,may be reinstalled in the same position by again threading the screwinto the hole such that the portion of it is received in theindentation.
 2. The combination according to claim 1 wherein the housinghas a front face; wherein the slot opens out of the front face; andwherein the deformable material forms a rim along the slot, with the rimprojecting beyond the front face.
 3. The combination according to claim2 wherein the rim on the housing contains the indentation and the headof the screw is received in the indentation.
 4. The combinationaccording to claim 1 wherein the housing has a front face and a backface; wherein the slot opens out of both faces and has side walls whichtaper downwardly toward the back face so that the slot is wider at thefront face than it is at the back face; and wherein the deformablematerial is located along the side walls of the slot.
 5. The combinationaccording to claim 4 wherein the indentation opens out of the taperedside walls of the slot and is configured to receive the shank of ascrew.
 6. The combination according claim 1 wherein the slot is one oftwo slots in the housing, and the slots are parallel; wherein thethreaded hole is one of two holes that open out of the mounting surface;and wherein the screw is one of two screws, with each screw being in adifferent slot and threaded into a different hole.
 7. The combinationaccording to claim 1 wherein the housing includes a sacrificial rimwhich projects beyond the sensing element a prescribed distance toestablish a known gap between the target and the sensing element.
 8. Aprocess for installing a speed sensor against a mounting surface out ofwhich a threaded hole opens so that the speed sensor can monitor therotation of a target that revolves in front of the mounting surfaceabout an axis oriented at a steep angle with respect to the surface, thesensor including a housing having a slot and along the slot being formedfrom a deformable material, the sensor further including a sensingelement located in the housing and being capable, in response torotation of the target, of producing a signal that reflects the angularvelocity of the target, said process comprising: placing the housing ofthe sensor against the mounting surface with the slot in the housingaligned with the threaded hole that opens out of the mounting surface;inserting a screw having a threaded shank and a head into the slot inthe housing; positioning the housing along the mounting surface with thecorrect gap between the sensing element and the target; with a portionof the screw forming a permanent indentation in the housing along theslot, with the indentation being configured such that, when the portionof the screw that formed it is in the indentation, the housing cannot bedisplaced along the slot; and threading the screw into the threadedhole.
 9. The process according to claim 8 wherein the head of the screwforms the indentation.
 10. The process according to claim 8 wherein thehousing has a front face; wherein the slot opens out of the front face;wherein the deformable material forms a rim along the slot, with the rimprojecting beyond the front face, and wherein the head of the screwforms the indentation in the rim.
 11. The combination according to claim8 wherein the shank of the screw forms the indentation.
 12. The processaccording to claim 8 wherein the housing has a front face and a backface; wherein the slot opens out of both faces and has side walls whichtaper downwardly toward the back face so that the slot is wider at thefront face than it is at the back face; wherein the deformable materialis located along the side walls of the slot, and wherein the shank ofthe screw forms the indentation in the side walls of the slot.
 13. Theprocess according to claim 8 and further comprising: withdrawing thescrew from the threaded hole; removing the sensor from the mountingsurface; thereafter placing the sensor along the mounting surface withits slot aligned with the hole; inserting the screw through the slot andthreading it into the hole, with said portion of the screw beingreceived in the indentation; whereby the sensor assumes the sameposition along the mounting surface.